Circuits for electromagnetic devices



Feb. 23, 1965 D. L. KING Em 3,171 065 CIRCUITS FOR ELECTROMAGNETIC DEVICES Filed NOV. 14, 1960 United States Patent 3,171,065 CIRCUITS FQR ELECTROMAGNETIC DEVICES Daniel Lawrence King, New Southgate, London, and Eric Gibbon Hitch, Enfield, England, assignors to Associated Electrical industries Limited, London, England, a British company Filed Nov. 14, 196i Ser.No. 69,125 Claims priority, application Great Britain, Nov. 26, 1959, 40,235/ 59 1 Claim. ((31. 317- -l4]t) This invention relates to circuits for electromagnetically operable devices, for instance relays, and has in view the provision of a circuit by which such a device can be released more quickly than it can be operated, or vice versa, as determined, by the circuit parameters.

To this end, according to the invention, an electromagnetically operable device has, an operating winding connected in a circuit comprising, a first resistance connected in series with the winding, a capacitance shunting the winding, and changeover contact means having two alternative positions, in one of which it connects the serial connection of said first resistance and the ca pacitance-shunted winding between supply terminals for the circuit, and in the other of which it instead connects a second resistance across the capacitance to provide a discharge path therefor.

In the operation of this circuit, with a suitable energizing source connected across the supply terminals and with the changeover contact means in the first of its two alternative positions, the operating Winding is connected for energization from the energizing source. Initially, however, energizing current will be diverted from the winding while the capacitance shunting it is charging: in consequence, adequate energization of the winding to operate the electromagnetic device will be delayed until such time as the capacitance reaches a state of charge at which the diverted current, reducing as the capacitance charges, becomes sufiiciently small to permit such operation. Since the charging current flows through the first-mentioned resistance, the operating delay will be determined by the time constant of the capacitance and this resistance. Conversely, with the changeover contact means changed to the second of its two alternative positions following energization of the operating winding the series connection including the winding is disconnected from the energizing supply, and energization of the winding is maintained only by the charge present on the capacitance. Consequently with the capacitance now connected to discharge through the second resistance, the efiective de-energization of the winding, and thus release of the electromagnetic device, will be delay-ed for a time determined by the time constant of the capacitance in conjunction with said second resistance and the impedance of the relay winding, which latter may be insignificant. It will therefore be evident that by appropriate selection of the relative values of the first and second resistances, the operating and releasing delays of the electromagnetic device may be predetermined such as to give the device either a fast operate/ slow release characteristic, or a slow operate/fast release characteristic as may be required.

The invention has important application in circuit arrangements in which an electromagnetic device which normally assumes one condition (namely its operated or unoperated condition) is required to change to and remain in the alternate condition for the duration of an impulse train applied to the arrangement. In describing a particular embodiment of the invention applied for this purpose, reference will be made to the single figure of the accompanying drawing.

Referring to the drawing, an electromagnetic device is shown as a relay R having an operating winding wI connected at one side to negative battery by way of a first resistance R1 and at its other side to the moving contact of a changeover contact set 21. One fixed contact of the contact set p11 is connected to (positive) earth, and the other fixed contact is connected to one side of a second resistance R2. The other side of the resistance R2 is connected to one side of a capacitance C which shunts the winding wl of the relay R. The contact set p1 is controlled by an impulsing relay P which has an operating winding w'2 connected at one side to negative battery and at the other side to an input terminal t to which impulses for causing operation of the relay P can be applied. In the absence of such impulses the relay P is normally unoperated, so that if the position shown for the contact set p1 is its unoperated position, an energizing circuit for the relay R is completed; with this energizing circuit thus normally established the capacitance C is fully charged.

When the relay P is caused to impulse by applying an impulse train to the terminal 1, the moving contact of the contact set p1 is actuated between the two fixed contacts of the set. On operation of the relay P, at the commencement of the first impulse, the contact set p1 interrupts the energizing circuit for the relay R and instead connects the resistance R2 across the capacitance C, which thereupon commences to discharge through this resistance R2. By making the time constant of the capacitance C and the resistance R2 such that the discharging period of the capacitance C is shorter than the period of each impulse, the capacitance C will become substantially discharged before the end of the first impulse and therefore the relay R will release. During the interval between the first and second impulses, the contact set p1 reestablishes the energizing circuit for the relay R, but initially energizing current will be diverted from the winding W1 to re-oharge the capacitance C. Therefore, by making the time constant of the capacitance C and in this case the resistance R1 such that the charging period of the capacitance C is longer than the time spacing of the impulses, that is, the interval between successive impulses of the impulse train, the capacitance C will be only partially charged and will he therefore still diverting the energizing current from the winding W1 at the commencement of the next impulse, so that re-operation of the relay R between the impulses will not take place. Discharging of the capacitance C then takes place during the period of this second impulse, followed by partial re-charging during the interval between this impulse and the third, and so on. In consequence, the relay R remains released for the duration of the impulse train, and does not re-operate until such time after the last impulse as the capacitance C becomes substantially fully re-charged and therefore no longer prevents operation of the relay by diverting energizing current from its operating winding wl. To fulfill the time constant requirements of the foregoing circuit the resistance R2 may have a relatively very low value, measured for instance in tens of ohms whereas the resistance R1 may have a value measured in thousands of ohms.

In a possible alternative mode of operation of the circuit, the relay R, being normally unoperated, may be arranged to be operated for the duration of an impulse train applied to the relay P. This mode of operation may be achieved simply by reversing the normal position of the contact set p1, so that the position shown is the operated position and the energizing circuit for the relay R is normally interrupted, and by modifying, on the other hand, the time constant of the capacitance C and the resistance R1 such that the charging time period of the capacitance C is significantly shorter than the period of each impulse, and on the other hand, the time constant of the capacitance C and the resistance R2 such that the discharging time period of the capaci tance C is significantly longer than the interval between impulses. In this case the relative values of R1 and R2 would be reversed, that is, R1 would be relatively low and R2 relatively high.

In this alternative mode of operation of the circuit, the capacitance C rapidly charges during the period of the first received impulse, leaving suifioient time for energization of the winding W1 and thereby permitting the relay R to operate, while during the interval between the first impulse and the second, the capacitance C only partially discharges, maintaining sufiicient charge to hold the relay R operated. During each subsequent impulse of the impulse train, the charge on the capacitance C is replenished and any decay of the energizing current in the Winding w1 is made good, so that operation of the relay R is maintained for the duration of the impulse train.

What we claim is:

In a circuit arrangement including an electromagnetically operable device which normally assumes one of two conditions and is required to change to and remain in the other condition for the duration of an impulse train constituted by impulses of predetermined duration and time spacing, an impulsing relay connected to receive said impulse train and to be repeatedly operated by pulses of said train and released during the absence of pulses, a first resistance, an operating Winding of said electromagnetically operable device connected in series with said first resistance, a capacitance shunting said winding, a second resistance, an energizing supply for said winding, and changeover contact means controlled by the impulsing relay between operated and unoperated positions, in one of which said contact means connects the serial connection of said first resistance and the capacitance-shunted Winding across said energizing supply, and in the other of which it instead connects the second resistance across the capacitance to provide a discharge path therefor, the time constants of the capacitance with the resistance with which it is connected in the operated and unoperated positions of the changeover contacts being chosen to be shorter than the duration of each impulse of said impulse train and longer than the time spacing of successive impulses in the train respectively.

References Cited in the file of this patent UNITED STATES PATENTS 2,101,166 Crago Dec. 7, 1937 2,608,608 Hands-chin Aug. 26, 1952 2,773,221 Shaw Dec. 4, 1956 

